Abstract: This study investigates the promotion logic, participation modes, existing problems, and optimization strategies of sports social organizations’ participation in extracurricular school-based sports services using methods such as literature review, field investigation, interviews, and comparative analysis. The study found that the government’s “administrative leveraging” mechanism,the realistic need of “the bidirectional dependence of resources” between schools and sports social organizations, and the alignment of the public goals of sports social organizations with school physical education represent the basic logic for comprehensively promoting the participation of sports social organizations in extracurricular school-based sports services. The compensating participation, complementary participation, voluntary participation and cost-based participation are four main participation modes of sports social organizations in extracurricular school-based sports services. The main issues in the current participation of sports social organizations in extracurricular school-based sports services include vague institutional regulations for different participation modes, underdeveloped operational mechanisms, cognitive biases among schools and the public, and inadequate capabilities of sports social organizations themselves. The high-quality promotion of sports social organizations’ participation in extracurricular school-based sports services urgently requires the integration of the four participation modes, reshaping schools’ understanding of sports social organizations, enhancing the participation capabilities of sports social organizations, and establishing a governance mechanism for sports social organizations’ participation in extracurricular school-based sports services.